Summer Training Report

SUMMER TRAINING REPORT

JSS MAHAVIDYAPEETHA

JSS ACADEMY OF TECHNICAL EDUCATION C-20/1, Sector-62, NOIDA-201301 (U.P)

Department of I & C

Compiled & Submitted By:-

Ashutosh Singh

(Univ. Roll No. 0509122010)

B.Tech (ICE), VII semester

[Summer Training Report On CNC Machines]

ACKNOWLEDGEMENT

We are highly thankful to B.H.E.L. engineers and technical staff for providing us vital and valuable information about the different facets of an industrial management system.

We express our gratitude to Human Resource and Development department for giving us a chance to feel the industrial environment and its working in B.H.E.L. and we are thankful to Mr. M.K.Nagaich, Sr.Engineer for giving his precious time and help us in understanding various theoretical and practical aspect of our project on CNC under whose kind supervision we accomplished our project. We are also thankful to Mr.Vijay Verma for his kind support.

Ashutosh Singh (B.Tech (ICE), JSSATE, NOIDA)

PREFACE

At very outset of the prologue it becomes imperative to insist that vocational training is an integral part of engineering curriculum. Training allows us to gain an insight into the practical aspects of the various topics, with which we come across while pursuing our B.Tech i.e. vocational training gives us practical implementation of various topics we already have learned and will learn in near future. Vocational training always emphasizes on logic and commonsense instead of theoretical aspects of subject.

On my part, I pursued four weeks training at B.H.E.L. Jhansi. The training involved a study of various departments of the organization as per the time logically scheduled and well planned given to us.

The rotation in various departments was necessary in order to get an overall idea about the working of the organization.

Ashutosh Singh (B.Tech (ICE), JSSATE, NOIDA)

BHARAT HEAVY ELECTRICALS LIMITED

In the post independence era when India was moving towards

industrialization, the thrust by the government was in the core sector.

With this objective BHARAT HEAVY ELECTRICALS LIMITED was setup

in Bhopal in August 1956, with a view to reach self sufficiency in

industrial products and power equipments. This plan was setup under

collaboration of M/s. AEJ, U.K.

Now more plants were setup at Tiruchy, Hyderabad and Haridwar

with Czechoslovakian and Soviet Union assistance in May 1956, Dec.

1965, and Jan. 1967 respectively. Today B.H.E.L. has become the

largest engineering plant employing approximately 72000

employees. Its headquarters are located at Delhi.

B.H.E.L. is the largest engineering and manufacturing enterprise

in India in the energy/infrastructure sector, today. B.H.E.L. was

established more than forty years ago ushering in the indigenous

heavy electrical equipments industry in India a dream that has been

more than realized with a well-recognized track record of

performance. It has been earning profits since 1971-72 and paying

dividends since 1976-77.

B.H.E.L. manufactures over 180 products under thirty major

product groups and caters to core sectors of the Indian Economy viz.,

Power Generation and Transmission, Industry, Transportation,

Telecommunication, Renewable Energy, etc. The wide network of

B.H.E.L.’s fourteen manufacturing divisions, four power sector

regional centers, over hundred project sites, eight service centers

and eighteen regional offices, enables the company to promptly

serve its customers and provide them with suitable products

efficiently and at competitive prices.

The quality and reliability of its products is due to the emphasis on

design, engineering and manufacturing to international standards by

acquiring and adapting some of the best technologies from leading

companies in the world, together with technologies developed in its

own R&D centers.

B.H.E.L. has acquired certifications to Quality Management

Systems- ISO 9001, Environmental Management Systems-ISO 14001

and Occupational Health and Safety Management Systems-OHSAS

18001 and has also adopted the concepts of Total Quality

Management.

B.H.E.L. has installed equipment for over 90,000 MW of power

generation- for Utilities, Captive, and Industrial users. It supplied over

2,25,000 MVA transformer capacity and sustained equipment

operating in transmission and distribution network up to 400 KV- AC

& DC.

It supplied over 25,000 motors with Drive Control System to

power projects, petrochemicals, refineries, steel, aluminum, fertilizer,

cement plants, etc. It also supplied traction electrics and AC/DC locos

to power over 12,000 Km railway network. Supplied over one million

valves to power plants and other industries.

B.H.E.L.’s operations are organized around three business

sectors, namely Power Industry including Transmission,

Transportation, Telecommunication and Renewable Energy and

Overseas Business. This enables B.H.E.L. to have a strong customer

orientation, to be sensitive to his needs and respond quickly to the

changes in the market.

B.H.E.L.’s vision is to become a world class engineering

enterprise, committed to enhance stakeholder value. The company is

striving to give shape to its aspirations and fulfill the expectations as a

Navratna Company.

The greatest strength of B.H.E.L. is its highly skilled and

committed 44,000 employees. Every employee is given an equal

opportunity to develop himself and improve his position. Continuous

training and retaining, career planning, a positive work culture and

participative style of management have engendered development of

a committed and motivated work force leading to enhanced

productivity and higher levels of quality.

VISION, MISSION AND VALUES OF B.H.E.L.

VISION:

A world class engineering enterprise committed to enhancing stakeholder value.

Mission:

To be an Indian Multinational Engineering Enterprise providing total business solution through quality products, system and services in the fields of energy, industry, transportation, infrastructure and other potential areas.

VALUES:

Zeal to Excel Zest for change.

Integrity and fairness in all matters.

Respect for dignity and potential of every individual.

Strict adherence to commitments.

Ensure speed of response.

Faster learning, teamwork and creativity.

Loyalty and Pride in the Company.

BHARAT HEAVY ELECTRICALS LIMITED, JHANSI

A Brief Introduction

By the end of five year plan it was envisaged by the planning

commission that the demand for power transformer would raise in the

coming years. Anticipating the country’s requirement B.H.E.L.

decided to set up a plant which would manufacture power and other

type of transformer in addition to the capacity available at B.H.E.L.

Bhopal. The Bhopal plant was engaged in manufacturing of

transformer of large rating and Jhansi unit would concentrate on

power transformer like instrument transformer, traction transformer

for railway etc.

This unit of Jhansi was established around 14 Km from the city on

the NH no. 26 on Jhansi Lalitpur Road. It was called second generation

plant of B.H.E.L. set up in 1974 at an estimated cost of Rs. 16.22 crores

inclusive of Rs. 2.1 crores for township. Its foundation was laid by Late

Mrs. Indira Gandhi, the prime minister on 9th Jan. 1974. The

commercial production of the unit began in 1976-77 with an output of

Rs. 53 lakhs since then there has been no looking back for B.H.E.L.

Jhansi.

MANUFACTURING UNITS OF B.H.E.L.

BHOPAL Heavy Electrical Plant

First Generation Units

HARDWAR Heavy Electrical Equipment Plant

HYDERABAD Heavy Electrical Power Equipment Plant

TIRUCHY High Pressure Boiler Plant

JHANSI Transformer and Locomotive Plant

Second Generation Units

HARDIWAR Central Foundry and Forge Plant

TIRUCHY Seamless Steel Tube Plant

BANGALORE Electronic Division

Unit Through Acquisition and Merger

Electro Porcelain Division

RANIPAT Boiler Auxiliaries Plant

New Manufacturing Units

JAGDISHPUR Insulator Plant

RUDRAPUR Component and Fabrication Plant

BANGALORE Industrial System Group

Focus

To build a high degree of customer confidence by providing

increased value for his money through international standards of

product performance superior customer service.

To enable each employee to achieve his potential, improve his

capabilities, perceive his role and responsibilities and participate

and contribute to the growth and success of the company, to invest in

human resources continuously and be alive to their needs.

People Orientation

To achieve technological excellence in operations by

development of indigenous technologies and efficient absorption and

provide competitive advantage to the company.

Technology

To fulfill the expectations which stakeholders like government as

owner, employees, customers and the country at large have from

B.H.E.L.

Image

THE PRODUCT PROFILE OF B.H.E.L., JHANSI

S.No. Products Specifications

1. Power Transformer Up to 220 KVA class 250 MVA

2. Special Transformer Up to 110 KVA

3. ESP transformer 1000 KVA

4. Fright Loco Transformer 3900-5400 KVA & 6500 KVA (3 Phase)

5. ACEMU Transformer Up to 1000 KVA 25 KV (single phase)

6. Dry Type Transformer Up to 3150 KVA

7. Bus Duct Up to 15.75 KVA (Generating voltage)

8. Instrument Transformer VT and CT up to 220 KVA

9. Diesel Engine Locomotive

Up to 2600 HP

10. AC/DC Locomotive Up to 5000 HP (25 KV AC/1500v DC)

11. Well Wagon 200 Tones

12. Over Head Equipment cum

Test Car

13. Dynamic Track Stabilizer

14. Ballast Cleaning Machine

GROWTH OF PRODUCTION AND MILESTONES

S.No. Year Milestones’

1. 1976-77 Start of Instrument Transformer Production

2. 1977-78 Start of Traction Transformer and Power

Transformer (Up To132 KV)

3. 1978-79 Start of HFTT type freight Locomotive

4. 1979-80 Commissioning of 2,500 KV DG Set

(Due to sever power cuts)

5. 1980-81 Start of ESP Transformer

6. 1981-82 Start of 220 KV Power Transformers

7. 1982-83 Achieve Break Even

8. 1983-84 Start of Bus duct

9. 1984-85 Start of Dry Type Transformer

10. 1985-86 Repowering of Diesel Locomotive Started

11. 1986-87 Start of Diesel Locomotive Started

12. 1987-88 Manufacturing Facilities for AC Locomotive

13. 1988-89 Crossed Core Target

14. 1990-91 Successful Design and Manufacturing of 400 HP 3

Axel Diesel CCI

15. 1991-92 Manufacture of First 2600 HP Diesel for NTPC

16. 1992-93 Successful Design and Development of

5000 HP Thruster Control Locomotive

17. 1993-94 Unit has been Awarded ISO-19001

Certificate for Quality Systems

18. 1994-95 240 MVA Power Transformer Produced First Time

19. 1995-96 AC/DC Locomotives first time in India

20. 1996-97 Hundredth Locomotive Manufactured

21. 1997-98 250 MVA Transformer Produced First

22. 1998-99 Developed Over Head Equipment cum Test Car

23. 1999-00 Diesel Hydraulic Shunting

ROTATION

REPORT

FABRICATION (BAY-0, 1, 2)

Fabrication shop is the shop which deals with the manufacturing of

transformer and locomotive components such as Tanks, Plates, and

Nuts and Bolts. Fabrication shop is divided into three parts-

BAY-0

BAY-1

BAY-2

This is the preparation shop, in this shop; we cut the different

components of the different materials as per the drawing

requirements. Different processing m/s in this BAY is as follows –

BAY-0

CUTTING MACHINE

a) CNC FLAME CUTTING MACHINE

By the use of this machine any shape can be obtained up to 2.5m to X7m.

Maker – ESAB Germany made

Flame – Oxy-Acetylene Flame

Feeding Language – ESSI Format, ESC Format

Capacity – 3.15mm to 300mm

b) Accuracy – 0.1mm

Cutting Tool – Copper

Materials to cut – Mild steel

c) PANTOGRAPH

d) PUG CUTTING

e) SHEARING

This machine is used for metal sheet. Cutting range is 2mm to 6 mm.

Suitable materials for use are Al, Standard steel and Cu.

BENDING MACHINE

Principle – Hydraulically operated

Pressure Gauge is used to read out the pressure applied. Stopping

mechanism is used by screw to prevent the collapsing the ram blade

with bending grooves (Die).

ROLLING MACHINE

This machine is used for decreasing the roll thickness. The roller

material used is High Carbon Steel.

It is having the two rollers and one bending roller. In this machine,

gears are used for speed reduction of the rollers to give uniform and

better thickness and good surface finish. Wedge type metal piece is

used (Manually operated) for changing the gap b/w rollers for the

required thickness.

FLATEENNG MACHINE

This machine is used to straightening the job. This is hydraulically

operated. In it, flattening load is applied by hydraulic method;

hydraulic oil of suitable grade is used. The capacity of this machine is

100 tons. The shape of ram is cylindrical.

RADIAL DRILLING MACHINE

In this machine, tool can move radically. In it cutting oil mixed with

water is used to cool the drill tool as used as the material to be drilled.

Different drill tools are used from 2mm to 100mm dia.

PLANO MILLING MACHINE

BAY (1, 2)

These BAYS are known as assembly bays. In these bays, different

operating is to be performed.

Fitting – In this section, as the name suggests, we fit different

components as the drawing requirements.

Welding – In this section, we weld the different components of

different drawing by permanent joints.

Testing – When our tank for the transformer is completed, then we

check the leakage tests on the tanks. There are two types of leakage

tests, which we have to perform on the transformer tank.

1. AT (Air leakage test)

In this test, first we fill the tank by compressed air and dip the tank in

the soap solution for bubble test.

2. VT (Deflection test)

Shot Blasting Plant-

When we check the leakage by satisfying result then we use SHOT

BLASTING for removing the carbon layer from the surface of the tank.

In the SHOT BLASTING, we use the small rings with the high pressure

of 7kg.

Painting –

After shot blasting, we paint the tank for corrosion resistant.

BAY -3

It is split in two parts, half is consist of machine shop and the other half

is consist of winding of dry type transformer.

There is different type machines used in section. These are listed

below.

1. Tool Cutter grinder – Used for cutting tool also grinding them.

2. Hydraulic surface grinder – It is consist of magnetic platform.

Cooling oils is used as coolant.

3. Drill sharp machine – It is used for sharp the drill bits by

means of grinding wheel.

4. Vertical grinder machine – It is used for grinding purpose.

5. Hydraulic power press – Used for straightening the material

capacity of this machine is 25 tones.

6. Resistance brazing machine – Used for overlap connections.

7. Bend saw machine – It is used for cutting circular object. In

this machine blade width is inch and thickness is ¾ inch.

8. Electric furnace – Used for heating the object.

9. Hydraulic punching machine – Used for making small pieces

of material for desire purpose. Range of this machine is

12mm to 250mm.

10. Hydraulic shearing machine – Used for cutting the material

in range between 12mm to 25mm.

11. Lathe machine – There are mainly three type of lathes are

there these are listed as below.

Turret lathe – Used for heavy duty. Range of this machine is

250mm to 300mm.

Capstone lathe – Used for light work, range of this machine is

20mm to 150mm.

Center lathe – It is used for light work and range of this machine

is 20mm to 200mm.

COPPER SECTION

This part is only concern with copper cutting, bending, tinning etc.

Machine used are as listed below.

a) Shearing machine: Range 4mm to 6mm and length of the blade is

830mm.

b) Hydraulic power press: Used for straightening the product.

c) Tube slitting machine: This machine is developed here and is

used for cutting the tube along its length and across its

diameter. Its blade thickness is 3 mm.

d) Fly press machine: It is fully mechanical and is used to press the

job. It is operated mechanically by a wheel, which is top on the

machine.

e) Lincing belt machine: It creates a smooth surface.

BAY – 4

Here winding work of the power transformer is carried out.

The coil of transformer is of four types.

a) Low voltage coil

b) High voltage coil

c) Tap coil

d) Tertiary coil

All the winding performed by the paper insulation copper conductor or by continuously transposed conductor it also made of copper. They can arrange by different ways.

a) Reverse section winding b) Helical winding c) Interlinked winding d) Half section winding

Figure showing Cast Resin Dry Type transformer find utilization in main power of industrial plants

Arrangement and type of coil depends upon job requirements. Also the width and thickness of the conductors are designed and are decided by design department. Conductors used for winding is in the form of very long spiral wound on a spool, conductor is covered by cellulose paper for insulation.

For winding first the winding mould of diameter equal to inner diameter of required coil is made. The specification of coil is given in the drawing section that interlocks with each other. This interlocking can be increased and decreased to adjust the inner diameter of coil. The moulds are of following types.

a) Belly types b) Link types c) Cone types

BAY – 5

It is core and punch section.

Core is the basic requirements of transformer in this bay various type of lamination of core is made, they are –

a) Side leg: - This lamination is at the extreme ends of the core which stand vertical. They are isosceles trapezium in shape with angle of 45.

b) Central leg: - This as the name suggests is central vertical portion of the core. It is diamond shaped with vertical edges longer. At the narrower edge one side is kept longer than the other for making a well fixed joint, the angles are kept 45.

c) Yoke: - The horizontal lamination of the core is called yoke. They are also isosceles trapezium in shape with angles of 45.

Slitting machine: It is used to cut CRGO sheets in different width. It

has a circular cutter whose position can be changed as per the

requirement.

CNC cropping line pneumatic: It contains only one blade which can

rotate 90º about the sheet. It is operated pneumatically.

CNC cropping line hydraulic: It is also used to cut the CRGO sheet it

contains two blades, one is fixed and other rotates 90º above the

sheet. It is operated hydraulically. M4 quality sheet 0.23-0.33 mm

thickness is used.

BAY-6

This shop is divided into two parts one is traction transformer winding and other one consist of assembly of traction transformer.

These transformers are used in locomotive used in the AC locomotive called freight locomotive transformer. These are mainly of two types: Single phase (5400 KVA) and Three phase (6500 KVA).

For local train EMV (Electrical multiple unit transformers) is to be used. These are also two type: Single phase (1000 KVA) and Three phase(1500 KVA).

The major difference is that it has various output terminals. The various outputs are required to supply the machine of different rating mounted on the loco. A tape changer is also provided and is used to obtain supply of different rating power.

Figure showing Transformer to be installed in Shatabdi Express Train.

The traction machine (DC Motor). Which provide torque to the loco etc by changing taps from the electrical panel on the driver desk the speed of the locomotive can be changed.

BAY – 7

In this bay various types of insulation are prepared which is to be

used in transformers.

MATERIAL USED:

a) Perma wood: Size 10mm to 50mm.

b) Precompressed: Size 1.5mm to 25mm.

c) Grey press board: Size 1.5mm.

d) Bakelite: Size 4mm to 25mm.

e) Fiber glass: Sixe 1mm to 3mm.

f) Epoxy glass: Size 10mm to 25mm.

g) N.B.C. sheets (Naporeniom bonded cork sheet): Size

3mm, 6mm, 10mm, and 12mm.

h) Silicon rubber: Size 1mm, 3mm, 6mm.

i) Nitric rubber: Size 3mm to 12mm.

PVA (poly vinyl alcohol) is used as additive.

MACHINE USED:

1. Rolling machine: It is used to roll the press board.

2. Hard press machine: It is used to build up any thickness plate. By heating plates and hardly pressed on this machine.

3. Circle cutting machine : It is used for cutting the circular objects and also used for machining

4. Scarfing machine: It is used for taper cutting.

BAY – 8

It is involved in manufacturing of instrument transformer of 132KV and

220 KV. Voltage Transformer, Current Transformer and ESP

transformer.

INSTRUMENT TRANSFORMER: These are of two types

a) Current transformer (C.T.)

b) Voltage transformer (V.T.)

CURRENT TRANSFORMER

It is step down transformer. High current is not directly measured but by the current transformer is step down to lower measurable values, which is generally low.

Body

• The main body is a bushing, it also act as insulator in which winding is placed.

• The CT has a bottom and top chamber. • The top chamber is the cylindrical tank of mild steel. It has

terminals for connection of HV coils. It has a glass window to indicate the oil level.

• Below the top chamber there is bushing made of porcelain. It has several folds and “rain sheds” to provide a specific electrical field distribution and long leakage path. Some bushings are of cylindrical while modern one is conical as amount of oil porcelain used is reduced without any undesirable effect.

• Bottom chamber house the secondary winding. There is also connection box to which the connection low voltage (LV) is made.

Windings

The primary winding consists of hollow copper/aluminum pipe bent from of ‘U’ aluminum, used for low rating. For higher rating a set of wire is passed through the pipe. For still higher rating, copper pipe is used and for highest rating copper pipe with copper wire passing through it is used. This arrangement depends on the current carrying capacity. The bent portion of primary as in the bottom chamber where as the free end is the top chamber. The straight portion lies inside the bushing.

The primary is wound with crepe paper insulation goes in increasing as we go downwards in the bottom chamber. The free ends are provides with ‘ferrules’, which are small hollow cylinder through which wires can pass connection to the primary are made through these ferrules. The secondary is divided in a number of coils for different set of tapings. Connections are different taping are made in connection box. Each coil has an annular core of CRGO (silicon steel).

VOLTAGE TRANSFORMER

This is also step-down transformer the out of construction is the same as that of C.T. It has also a top chamber, bushing and a bottom chamber. The difference is only in windings.

Windings

The primary winding is of thick wire having a few turns. The winding is heavily insulated with paper insulation. It has a hollow cylinder passing centrally through it, which houses the secondary winding. The clean and painted with either enamel or epoxy paint. The costumer gives the choice of paint. Epoxy paint is generally used in chemical plant and seashore installation. Terminals are then mark and rating and diagram plate is fixed. The job is sent to shipping department which takes care of its dispatch by packing in the wooden boxes.

DIFFERENCE: - In current transformer, primary has less turns then secondary and vice versa.

ESP TRANSFORMER: -The Electro static precipitator rectifier transformer is used for environmental application. It is used to filter the suspended charged in the waste uses of an industry. They are of particular use in thermal power station and cement industry.

The ESP is a single ø phase transformer. It has primary and secondary windings. The core is laminated and is made up of CRGO sheet. It is a step up transformer. An AC reactor is connected in series with primary coil. The output of the transformer must be DC which is obtained by rectifying AC using a bridge rectifier (bridge rectifier is a combination of several hundred diodes). A radio frequency chock (RF chock) is connected in series with the DC output for the protection of secondary circuit and filter circuit. The output chosen the negative because the particles of carbon are positively charged. The dc output from the secondary is given to a set of plate arrange one after the others. Impurity particles being positively charged stick to these plates, which can be jerked off by hammer. For this a network of plant has to be set up all across

the plants .This is very costly process in comparison with the transformer cost. A relevant is also provided to prevent the transformer from bursting it higher pressure develops, inside it. It is the weakest point in the transformer body. An oil temperature indicator and the secondary supply spark detector are also provided. One side of the transformer output is taken and the other side has a “marshalling box” which is the control box of the transformer.

BAY – 9

Three types of transformer are fabricated in this bay:

1. Power transformer.

2. Dry type transformer.

3. Rectifier type transformer.

1) POWER TRANSFORMER

Power transformer find their wide use in electrical power system. Actually these are the transformer, which have made A.C. transmission very easy. These are step up or down transformer. The primary and secondary voltage of power transformer comprises material for magnetic circuit terminals, tanning switches, tank oil as well as cooling devices.

A power transformer undergoing testing in BAY-9 is shown in above figure.

2) CAST RESIN DRY TYPE TRANSFORMER

The cast resin dry type transformer consists of high voltage and low voltage winding made of Cu conductors which are completely impregnated and cast under vacuum. The glass fiber epoxy insulation of very good electrical and mechanical quality is used. Both HV and LV windings are separately as one solid coil, the iron coil is made from lamination of CRGOS. Bushing of cables boxes are provided for HT and LT connections.

These transformers are used in under substation, high building and hotels under the roof installation power plant etc.

3) RECTIFIER TRANSFORMER

In some industries electrical energy is supplied in the form of the direct current. Rectifier transformer along with other equipments is used to convert AC to DC. The advantages of using the rectifier

transformer along with rectifier unit efficiency are that it can be connected to the supply lines. This being static unit efficiency is high.

It may appear to be power transformer, but it differs in many respects, power transformer is used to step up or down the voltage where rectifier, secondary of which corresponds to the output DC voltage.

The quality that makes a rectifier transformer unique is:

The LV of a rectifier transformer carry very high current busher has to be used for the connection winding and terminals.

Other associated equipment of rectifier transformer is also housed in the same tank. A rectifier transformer is basically a constant current transformer and consequently KVA rating changes with output voltages.

The rating of a transformer is in watts greater than the rated DC power output is required to provide for the harmonic current of distorted waves.

TESTING

TRANSFORMER TESTING

In this shop testing on the transformer is carried out in one section and for loco in other section. In transformer testing section there are for MG. sets. The electrical specification of the entire test is already given. These tests are done on demand of customer on transformer manufactured, in this unit there are basically of test.

1. TYPE TEST – This test is done in a single unit of that type.

2. ROUTINE TEST – Bach and every unit has to be tested

individual.

(a) For power transformer – routine test

Ratio test: Special equipment transformer from

routine meter.

Resistance test: Special equipments – Kelvin and

Wheatstone bridge.

Insulation resistance test: Special equipment megger.

Separate source voltage withstand test: Special

equipments – HV transformers with associated control

and measuring desk, standard capacitance potential

divider.

Iron loss measurement test : Special equipment :

• Electro dynamometer

• RMS voltmeter

• Average voltmeter

• Precision class measuring VT

• Variable frequency sine wave generator

TEST OF CURRENT TRANSFORMER

1. POLARITY TEST :

• INSTRUMENT USED: Polarity meter analog multimeter

One of the winding is supplied with 1.5V D.C supply and other is

connected to ammeter. If the direction of the deflection is correct

implies the connections are correct else it is wrongly connected.

2. ACCURACY TEST :

It is the test for checking the turn ratio steps:

A standard transformer primary is connected across

the primary of the job.

As the no. of turns of the secondary transformer is

known the no. of turns of secondary of job is

calculated.

The ratio is taken and the max permissible error

should be not more than that specified by the design.

Even the phase angle is checked for this max

permissible limit.

3. INTER TURN INSULATION TEST :

Checks for the insulation of the transformer

Current is given to primary and secondary is open

circuited.

Either of the rated primary current or the 4.5KV peak

secondary voltages whichever appears first is

allowed to withstand for 1 min.

Then if the insulation can withstand then it is said to

be okay.

4. WINDING RESISTANCE :

Error in winding resistance appears if the conductors of different

length are used if the conductors are joined in between to check this

winding resistance is checked and if it appears then the internal

points of connections is changed.

TRANSFORMER COMMERCIAL (TRC)

The objective of this department is to interact with the customers. It

brings out tenders arid notices and also responds to them. It is

department that places the contracts of building the transformer and

after delivery further interacts with the customer regarding faults,

failure and maintenance is done by this department. All such snags

are reported to them and they forward the information to the

concerning department.

The works of the commercial department are:

Tenders and notices

Interaction with design department

Place of work

Approximate cost of the work

Earnest money

Place and time where contract document can be seen.

Amount if any to be paid for such document

TENDERS AND NOTICES:

The department response to the tenders calls of companies or

organization which requires transformer. Contracts are bagged

through negotiations.

The department also invites tenders and notices. Before inviting

tenders it must be sure that BHEL is ready to undertake the contract

and before full knowledge of scope of work is essential.

The transformer manufactured in BHEL Jhansi range from the 10MVA

to 240MVA and up to 200 KV. The various transformers manufactured

in this unit are:-

TRANSFORMER ENGINEERING (TRE)

Power transformer

Generation transformer.

System transformer.

Auto transformer

Special transformer

Freight loco transformer.

ESP transformer

Instrument transformer

Dry type transformer

All above types are oil cooled except dry type, which are air-cooled.

The generation voltage stations are 6.9KV, 11KV and 13.8KV but due

to certain advantages like economical generation 11KV is the most

widely used. For this voltage needs to be stepped up. Transmission at

high voltage is desirable because it results in lesser losses, needs

thinner wire and hence is economical. If the current kept high the

copper losses become very high but iron losses are practically

constant.

In certain cases the required voltage may be less than the output

voltage, so in order to obtain it were required a tapping circuit. The

output may have a certain percentage variation, which may be tapped

in 4 or 6 equal steps. The type of tap changer depends on the

application of the transformer. Where a continuous power supply is

not required an Off Circuit Tap Changer (OCTC) may be used. Where

a continuous power supply is must e.g. at substation in cities etc. On

Load Tap Changer (OLTC) is used.

TECHNOLOGY

This department analyses the changes taking place in the world and

suggest changes accordingly. This is very important because the

product must not get obsolete in the market otherwise they will be

rejected by customer.

Function: Technology function can be classified as:

Processing sequence: The sequence of process of

manufacturing is decided for timely and economic

completion of the job.

Operation time estimate: It includes incentive

scheme management.

Allowed operation time: It includes incentive

amount.

Facilities identification: It includes looking for new

equipment, plant or tools to increase productivity.

Special process certification: Special processes are

the once required expertise for example identifying

errors, cracks, air bubble in winding.

Special tool requirement: Special tools are allotted

if possible. When required else the design has to be

reconsider.

Productivity projects compilation: It includes the

initial analysis of the problem and their appropriate

solution to enhance productivity.

The principle of working is that “IF YOU DON’T MAKE CHANGES IN

YOUR COMPANY, THE COUSTMER WILL CHANGE YOU”.

BUS DUCT

Bus duct is used as connection between generators and

transformer. Bus duct are used in power connection over 150 M V.

The question now arise that why are bus duct preferred over normal

conductors. In high power application, insulations are the major

problems and frequent insulation breakdown occurs. If this does

happens then possibility of shorting of conductor’s and hence serious

damage may occur to both transformer and generators.

Bus duct are hollow pipes made of aluminum the cross section of

these ducts depends on requirements of the customer and is done by

the design department.

The cross section may have different shapes, circular, square

hexagon, octagon. The casing is also made of aluminum sheets.

Although aluminum is not a good conductor as copper still is preferred

over it because it is lighter than copper. Moreover, it is cheaper than

copper.

Bus duct are of two types:

a. Segregated Bus Duct(SBD)

b. Isolated Bus Duct(IBD)

In segregated bus duct one casing is divided into three separate

chambers for the three phases. In isolated bus duct is provided into

separate casing. The conductors i.e. duct is separated from the casing

by proclaim or epoxies (chemical) insulators.

Bus duct assembly contains three cubicles

P.T. and S.P. cubicles

N.G. cubicles

L.A.V.T. cubicles

These cubicles have the circuit and the controls of the bus duct

assembly. The connection may be star or delta. The lines enter

from the top of the chamber. The top chamber has the neutral side

and the line side. The aluminum conductor in bus duct is not solid

because of ac has skin effect i.e. it flows only on outer surface of

conductor then why to waste money on the remaining conductor,

so we simply remove that part so it is hollow conductor.

LOCOMOTIVE

A locomotive is a rail vehicle that provides the motive power for a train.

“Loco” means from a place

“Motive” means causing motion.

A locomotive has no payload capacity of its own. It is used to move a

train.

The trains which have self propelled pay load carrying vehicles are

called Multiple Units (MU) or rail cares.

By their use:

CLASSIFICATION OF LOCOMOTIVE

Passenger Locomotive

Fright Locomotive

Shunting (switcher) Locomotive

By their source of energy

Steam Locomotive

Diesel Locomotive

• diesel electric

• diesel hydraulic

Electric Locomotive

Magnetic Levitation

Hybrid Locomotive

Steam Locomotive

Less efficiency in comparison to electric and diesel locomotive

Requires more manpower to operate.

Use in countries where coal is much more abundant source than

diesel fuel.

Use at mountains and high attitudes rail lines as they are less

affected by reduced air pressure.

Diesel Locomotive

Powered by internal combustion engine.

Power Transmission-output of prime mover to driving wheels.

• By coupling Alternator/Generator to prime mover. (Diesel

Electric)

• By coupling torque converter to prime mover. (Diesel

Hydraulic)

Requires less maintenance as compared to steam locomotives.

Electric Locomotive

Electric power supplied extremely through an overhead pickup

(centenary) or through a third rail.

High performance and low operation cost.

Capital cost of electrifying track is high.

Speed up to 575 km/hr.

Can also operate on battery power.

Battery locomotives which are used in mines and underground

location.

Magnetic Locomotive

New technology in train.

It floats the train above the rail without wheels.

Reduce friction.

Cost is very high.

Hybrid Locomotive

Used on board rechargeable energy storage system.

Locomotives manufactured at BHEL

Electric Locomotives

WAG-5

WCAM-2 AC/DC

WCAM-3 AC/DC

WCAG-1

Main customer: INDIAN RAILWAYS

Diesel Shunting Locomotive

Diesel Eclectic

350HP DESL

450HP DESL

700HP SPP/TPP DESL

1150 DESL

1350 DESL

1400 DESL

2600 DESL

Main customer: Power plants, Steel Plants, Cement Plants, Coal

Mine, Port trust and Fertilizer plants.

Diesel Hydraulic Locomotive

Figure showing a 25 KV AC/1500V DC AC/DC locomotive type WCAM-3

800 HP DHSL

Customer: IFFCO, Kandala

Battery Locomotive

450 HP

Customer: DMRC, New Delhi

New Products

OHE recording test car.

200MT well wagon.

Rail cum Road Vehicle (RRV).

Utility Vehicle.

Diesel Electric Tower Car (DETC).

Battery Powered Road Vehicle (BPRV).

Synchrolift Hoist Assembly.

Dynamic Track Stabilizer (DTS).

Ballast Cleaning Machine (BCM).

Figure demonstrating 700 hp twin power-pack DESL.

Main Parts of Diesel Locomotives

Under Frame: The one on which a locomotive is built.

Super Structure: The body of locomotive is called superstructure

is made of sheet of mild steel.

Bogie: The wheel arrangement of loco is called bogie. A bogie

essential contains.

• Bogie frame

• Wheel and axle

• Traction motor

• Gear and pinion

• Brake shoe

• Pull rod

• Sand box

• Springs

• Brake cylinder

Main Equipment of DESL

Traction Alternator/Generator.

Traction Motor.

Blower.

Compressor or Expresser.

Switchgear Equipments

Drive Desk.

Fuel Tank.

Batteries

Radiator

Brake System

Simple Air Brake System.

Air Brake System with MU operation

Air Brake System with MU Operation and air break on trailing

stock.

Dual Break System-Air and Vacuum.

Energy Transmission

In DESL In DHSL

Mechanical Energy Mechanical Energy

Electrical Energy Hydraulic Energy

Mechanical Energy Mechanical Energy

Traction Transformer: It is fixed on under frame and gets supply from

an overhead line by equipment called pantograph. The type of

pantograph depends on supply. This transformer steps down voltage

and is fitted with a tap changer. Different taps are taken from it for

operating different equipment. One tap is taken rectified into DC

using MSR and is fed to the DC motor.

STORE

There are three sections in store :

Control Receiving Section

Custody Section

Scrap Disposal Section

Functions: A list of material coming in store is prepared and Quality

Control people are called for inspection. If material is found as par

standard SRV (Store Receipt Voucher) is issued for each material. A

total of 08 SVR’s are prepared. Some materials such as Silicon oil,

Transformer oil, insulating material etc are directly stored in the Bays.

CENTRAL QUALITY SERVICE

First we get acquainted with a few terms concerning this department.

Quality: It is the extent to which product and service satisfy the

customer needs.

Quality assurance: All those plants and systematic action necessary to

provide adequate confidence that the product or the service will

satisfy the given requirement is called quality assurance.

Quality control: Activity such as measuring testing, gauging one or

more characteristics of product or service and comparing these with

specified requirement to determine conformity are termed quality

section.

WORK ENGINEERING AND SERVICES (WE&S)

As the name suggest this section deals with services and maintenance.

It has following Sections:

Plant Equipment: This has electronics and electrical/mechanical

maintenance.

Services: This section deals with air, steam and power

equipments.

Telephone Exchange:

Township Electrical Maintenance:

WE & S Planning

This section deals with stores and new machines

procurement and others general things. There are three maintenance

centers at Bay 2, Substation and LOCO. This section is also

responsible for power distribution is of two types:

HT POWER DISTRIBUTION: This is at 11 KV, OCB are used for

protection. There are four substations for this distribution.

LT DISTRIBUTION: This is for the auxiliary in each shop and other

section of BHEL. It uses OCB/OVB/ BHEL (Bhopal), 800 KVA, 11

KVA 45 V transformer and ACB (English Electro).Transformer

Supplied with enclosure of IP 23 class of protection. Bushing of

cables boxes are provided for HT and LT connections.

These transformers are used in underground substation, high

building and hotels, under the roof installation, power plant etc.

PROJECT REPORT

ON

“CNC MACHINES”

INTRODUCTION AND GENERAL WORKING OF CNC MACHINE

CNC machine tools have been widely accepted as time proven manufacturing technique all over the globe. In India too, CNC machine have picked up momentum and Indian Industries are going for more and more CNC machine.

Numerical control turns machine tools into a flexible production unit with a multitude of possible application. Although at first they were mainly used for manufacture of geometrically complicated parts, numerical control were later used for added enhanced efficiency in the medium batch production of turned and milled parts. The next step is the introduction of numerical controls in all sections of productions. The aim in all the cases is to combine high productivity with flexible possibilities of NC technology.

Other machine processes are being added to turning and milling which may be already described as classical NC applications. Conventional methods are being replaced by NC for sheet metal-working processes of punching, nibbling and cutting. Productivity increases multifold using numerical control with grinder, gear hobbers and spark erosion.

ELECTRONIC REVOLUTION AND COMPUTER GROWTH

Modern day computerized numerical control system (CNC) is the result of advancement and sky rocketing microelectronics with every day breaks its own record and grow by leaps and bounds. Initially NC machines had as many as 280 printed circuit board (PCB) and quite extensive wiring which consequently made maintenance very difficult and reliability was poor. First generation NC system had transistor elements.

With advent of integrated circuits only 40 PCBs were used with reduced wiring for the system. Further integration called ‘Medium Scale Integration’ (MSI) replaced nearly 10 ICs and system involved only 5 to 10 PCBs. With arrival of what is known as age of “Microprocessors and Very Large Scale Integration (VLSI) technique” ,modern day CNC machines use only 2 to 4 PCBs. The trend with microprocessors helps in lowering cost of jobs and increment in reliability to appreciable label.

Flexibility as inherent feature of minicomputer and microcomputer gave new technology –“Software Oriented System”.

Unlike rigid hardwire system which had been used hitherto, this new system comes to market as COMPUTER NUMERICAL CONTROL (CNC) system.

With this latest technology, hardware cost of CNC system lowered considerably whereas flexibility increased multifold due to software capabilities.

Electronic industries association defines numerical control as “A system in which action is controlled by direct insertion of numerical data. The system must automatically interpret at least some potion of data.”

WORKING PRINCIPLE OF NC MACHINES

In simple word numerical control means control by numbers. In NC machine tools the main function is to control the displacement and positioning of slides, spindle, speed, feed rate, selection of tool and many other auxiliary functions. NC directs the machine tool to achieve all these function in a very controlled and systematic manner .The major elements that comprises NC machine tools are :-

Control system – CNC

The machine tool

Servo drive units

Feedback devices

Operator control

Electrical cabinet

Schematic diagram representation of NC machine tool

In CNC system, tape instructions are read by tape reader. These instructions undergo electronic processing and system gives output in the form of electrical signal to servo drive of the machine tool to determine the length of movement and feed rates. System also directs commands to various relays, solenoids etc to initiate operation of the machine tools such as spindle motor starting and stopping , coolant supply , auto tool change and other miscellaneous functions.

Once the machine tool has commenced its operation and operative element and moving , it become necessary to ensure that required lengths of movements have taken place or a particular function has been accomplished. This is done by feedback devices. Position feedback devices like linear scales, encoder, resolvers, inductosyn feedback status of actual position of slides to control system. A

velocity feedback transducer known as ‘Tachogenertor’ is used for velocity control as warranted during contouring operation . Feed back of auto tool change function etc are taken from proximity sensors or limit switches. Thus all operations of machine are monitored continuously with appropriate feedback devices. In case of failure or adverse feedback received by system , machine stops and system displays ‘Fault message’ in clear English text.

TYPES OF NC

Based on feedback, NC system can be broadly classified in two types as ‘Open loop’ and ‘closed loop’. The open loop system has no feedback, whereas closed loop system utilizes feedback transducers which continuously monitor the position of slides. This enable machine to achieve a very high degree of accuracy in slide displacement

Figure above showing open loop system.

From metal removal point of view, the classification can be made as point to point, straight cut and contouring system. In point to point system, the machine performs machining operations at specific positions and does not affect work piece while moving from one point to another. An example of this type is NC drilling machine.

Straight cut or straight line system provides movement at controlled feed rate in one axis direction at one time. The examples of this are face milling, pocket milling etc.

Figure showing closed loop system.

Figure demonstrating NC system’s some of different paths and cut.

The continuous path control system calls for co-ordinate movement of the tool and work piece along different axes. This enables machining of complex profiles, contours and curved surfaces.

In a NC machine certain design features are desirable on machine tool. Simultaneous movement of 2 or more axes and high removal capability of NC machines demand high dynamic stiffness in drives and also stiff structural elements. The structure of NC machines should be very rigid to withstand heavy cuts and it must be maintained for long time to obtain high accuracies.

MACHINE TOOL REQUIREMENT

High positioning accuracy needed in NC machine make it essential to have backlash free screw and nut and slides with a very low friction of co-efficient. This is achieved by ground re circulating ball screw and nut, tachoway bearings, hardened and ground guideways and friction reducing linears such as Turcite and PTFE.

Electronic spindle drives on NC machines facilitate step less speed over a wide range of RPMs.

All axes are driven by powerful DC Servo drives controlled by PWM or SCR controllers through preloaded ball screw and nuts.

Automatic tool changer, centralized lubrication system, index table or fourth axis is common features on NC machines.

CNC machines ensure better and consistent accuracies on job compared to conventional machines. Positioning accuracies to be extent of +10 or -10 microns and repeatability of +5 or-5 microns can be achieved in NC machines depending on the elements used.

ACCURACIES

Parts Suitable For CNC Machines:-

To utilize the CNC machine effectively and economically the suitable pats selection is very important, the following guidelines should be observed:

High number of operation per component.

Complexity of operation.

Size of batches medium.

Repetitions of batches are often.

Labor cost of component is high.

Requires substantial tooling.

Requires 100% inspection.

Setup and inspection time is high.

Ration of cutting time to non-cutting time is high.

Varieties of components produced are more.

Skilled required by operator is high.

When a company or organization first decides to buy CNC machine, Orientation at all material level is required to get maximum return out of huge investment made. It is not sufficient that management understands the benefit of machine and decided to buy one, instead a deep insight of CNC technology is must and will quite obviously helps in buying suitable one and keeping its idle time minimum. Following Are few point for effective utilization of CNC machine.

GUIDELINES FOR EFFECTIVE UTILIZATION OF CNC MACHINES

It is vital that time taken for machine to become productive is as short as possible. The key to good CNC machine lies in prior planning, which should start the day management decides to buy CNC machine.

Programmers, maintenance people and operators should be selected and trained before CNC arrives.

Foundation and electric supply requirement should ready before machine arrives.

For small organizations where experts and maintenance staffs are generally not available, proper support from supplier should be ensured.

It should be ensured that suppliers of NC machines provide with all relevant technical documents for the machine.

While NC can be out product its manual counterpart 3 to 4 times, you can just easily loose this multi machine capacity during breakdown. To keep downtime minimum, sufficient quantities of spare are recommended by suppliers of machine should be maintain. Also it is always make sure that supplier of machine stocks critical parts and accessories.

Sufficient thought should be given to tooling, accessories and all other peripherals that surround CNC.

CNC machines must be placed at convenient places in the shop considering work flow and material handling. We can’t keep NC machine waiting while we are searching for tools or waiting for availability of raw materials.

Future expandability should always be in decision making while buying a CNC machine.

Clean and dust free environment should be ensured in shop in order to minimize breakdown efficient working and consequently longer life of CNC machine.

GENERAL INTRODUCTION TO MECHANICAL AND HYDRAULIC ITEMS

MECHANICAL ITEMS

1. Re-circulating linear roller bearing (Tychoways)

Good performance, high precision and high efficiency are quite obvious requirements which CNC machines are required to fulfill. Preconditions are basically good performance; high precision and high efficiency are minimum wear rigidity and low friction. These conditions are fulfilled by re circulating linear roller bearings.

The main characteristics of these bearing are continuous roller circulation which follows unlimited linear movement and elimination of the stick-slip effect which makes accurate positioning of machine, possible.

Tychoways consists of hardened, high precision machined, supporting elements, head pieces which are screwed on to the front face, and a number of cylindrical rollers. As with cylindrical roller bearings, the rollers are guided between the shoulders of the supporting elements with a very close tolerance. Therefore skewing the roller and resulting the additional friction as well as the forces acting at the right angle to the rolling direction can be avoided to a large extent. The retaining element made from the plastic material and situated between the rollers not only prevents the roller from falling out and sliding against each other but also results in smooth return of rolling element to the return zone.

Elastic strippers which are built into head pieces provide the bearing with effective protection from foreign matters.

Tychoways are suitable for grease and oil lubrication and can be used in temperature range from – 30 degree to 90 degree.

2. Torsionally stiff coupling

These flexible coupling without backlash are specially designed for servo or variable speed drives. They guarantee an accurate transmission for angle of rotation even in presence of alignment

errors e.g. between motor shafts and ball screw of machine tools. The special design for metal body allows a high torsional stiffness which frequently exceeds the motor shaft itself. The bearing load is kept low due to low lateral spring load stiffness. The conical hubs provide a positive detachable connection between coupling and shaft, without use of additional elements. Since there are no parts subject to wear, couplings are maintenance free.

3. Angular contact ball bearings for spindle

Ball bearings for machine tools must support radial loads combined with thrust loads in either direction. For this reason preloaded, angular contact ball bearing are generally used. These bearings are available with high (25 degree) and (15 degree) contact angles. In selecting the proper sizes and type bearing, consideration is given to size and construction of spindle and the kind of mounting, since the latter relates directly to the contacts spindle rigidity and deflection characteristics.

In general where the operating load is principally radial, low contact angle type bearings are selected, but where the loading is chiefly in thrust and high degree of axial rigidity is required, higher contact angle type of bearings are recommended.

Also three bearings are preloaded to reduce axial and radial deflection and may be mounted in three different arrangements

i) Back-to-back

ii) Face-to face

iii) Tamdem

In back-to –back (D3) mounting, the most commonly used the stamped faces of the bearing outer ring project beyond the inner ring and about each other. The angular line of contact of these bearing diverges in direction of rotation of axis, resulting in both axial and radial rigidity of the shaft and providing maximum rigidity to the deflection. Upon clamping the inner ring together by tightening the inner ring locknut, a load is imposed through a ball and the outer rings. This takes up the internal clearance and places these members in compression. The initial amount of offset or clearance between the inner ring faces, therefore, determines the amount of preload.

When bearings are mounted face-to face (DF) that is with the unstamped faces of four rings together, the angular lines of contact of bearing converge in direction of rotational axis and the inner rings project beyond the narrow faces of the outer rings. When the outer ring is clamped together, the initial clearance between the outer rings is taken up, preloading the bearing.

Different mounting arrangement for angular contact ball bearing

Duplex preloaded bearings mounted in the tandem (DT) divide the work load between the bearings. So arranged, with the angular lines of contact of bearing parallel and in tandem, they must be opposed by another bearing or a pair of bearings, to provide axial stability to the mounting.

4. Ball and screw nut

In ball screw, a screw runs on bearing balls, the screw thread is actually a hardened ball race. The nut consists of series of bearing balls circulating in similar race and carried from one end of the nut to other end by return tubes. The balls provide the only physical contact between screw and nut, replacing the sliding friction of conventional screw with a rolling friction.

4.1 High efficiency and reversibility

FEATURES OF PRECISION BALL SCREWS

The high mechanical efficiency (over 90%) of ball screws results from rolling contact of precision bearing balls and precisely ground threads of screws. As compared to relatively low speed sliding friction of conventional Acme screw, the power requirement for ball

screw is low because of high efficiency of ball screws are reversible which makes it possible to back drives the unit by applying the axial force to either nut or screw then rotating member is not restrained. In this way, the unit can be used to convert a axial force into a rotator torque.

4.2 No Stick Slip

Substituting rolling contact for sliding metal to metal contact minimizes starting friction, eliminates the static slip tendency where a slow speed linear motion is required.

4.3 Wear and Life

The balls rolling in the hardened grooves reduce wear to minimum, eliminating any need for frequent compensating arrangement and adjustment. Ball screws therefore, for years without any detectable change in accuracy of system.

4.4 High Stiffness and Little Axial play

When axial is minimized in conventional nut screw assemblies, the actuating torque becomes excessive and operation is not smooth. This axial play in ball screws may be reduced to zero preloading and a light smooth operation is still possible. Therefore both low torque and high stiffness can be achieved simultaneously.

In view of life and efficiency, ball screws require adequate lubrication which may be either greasing or oiling.

LUBRICATION

For greasing, grease based on lithium soap is usually recommended and for oiling, turbine oils with viscosity from 38 cst to 90 cst are recommended.

HYDRULIC ITEMS

SINGLE SOLENOID SPRING OFFSET DIRECTIONAL CONTROL VALVE

This valve is used to control the direction of flow with the help of valve spool. A cylindrical spool moves back and forth in machine bore and in valve body. Cored or machined passages from the port connections in the valve body are interconnected through annular grooves (undercuts) in the spool or blocked by spool lands.

The valve spool is shifted by energizing a solenoid at one end of the spool. When the solenoid is de-energized the spring at the opposite end of the spool returns the spool to its original position. This is a two position valve and a spring returns the valve to one extreme position. That’s why the valve is called spring offset.

These direct operated solenoids are kept in DC4 series by Vickers. Ports connections are made by means of sulphate permitting any easy removal of valve body for service and replacement. The solenoid is self contained and self controlled push type unit which bolts to the end of the valve body. These valves are rated in the 10-20 gpm range.

Graphical symbol for valve

Since there are two operating position and 4 connections this is also known as 2/4 directional valve.

A schematic representation is shown below:

In this type of valve there are three positions of valve spool. Control spring acting on the both ends of the spool keeps it to the central position when both solenoids are energized. To hold on extreme position one solenoid should be continuously energized.

DOUBLE SOLENOID SPRING CENTERED DIRECTIONAL CONTROL VALVE

These valves are also kept in DG4 series by Vickers. The schematic representation by this valve is shown in figure below:

And its graphical symbol is:

The valve in the figure shown above is in central position. In this position the central port is closed and port A and B are open to tank.

Since there are 3 positions and four connections it is also called ¾ directional valve.

In all solenoid electric energy supplied to the coil create magnetic field by virtue phenomena of electromagnetic induction, which consequently draws armature into the coil. The armature motion in turns push rod or can be seen as transmitted via push rod which in turns moves the spool.

PRESSURE OPERATED CHECK MODULE

These modules contain a check valve in both cylinder portion check valve allows free flow of oil in one direction. They are arranged for free flow out of the directional valve.

For return flow one check can be unseated by a common striker piston, mounted co-axially between two checks. This happens when internal pressure on one side is sufficient to cause the striker piston to open the check valve on the other side. At neutral position, compression spring will seat the check and machine actuator will be held stationary.

Within each poppet piston, is a small decompression poppet which opens before the main check valve.

NON PRESSURE COMPENSATED FLOW CONTROL VALVE

(WITH CHECK VALVE)

Flow control valves are used to regulate the speed of actuator by controlling the flow of oil from the pump. There are three basic methods of applying volume control valve in a circuit

a) Meter-in

b) Meter-out

c) Bleed-off

In meter-in operation, the flow control valve is placed between the pump and the actuator. In meter-out it is located in the tank line. In bleed-off arrangement the flow control valve is kept in the pressure line and diverts excess flow to the tank, thus permitting only require flow pass through actuator.

Meter-out control finds advantage over the others in the NC machines. If the load turns to “run away” it will it will regulate actuator speed because it restricts exhaust flow from actuator. Other advantage is that being in a low pressure line losses are less.

A check valve is incorporated for free flow in reverse direction.

The figure above demonstrates the meter-out flow control……

Graphical symbol along with the internal construction of non-compensated flow control valve.

NON-COMPENSATED DUAL CONSTRUCTION FLOW CONTROL VALVE

It regulates flow rate between DG 4 (4 way valve) and hydraulic actuator.

Graphical representation of this valve is shown in figure….

Dual valve construction permits free flow to both actuator port and adjustable independent flow regulation in each return line from actuator.

PRESSURE AND TEMP. COMPENSATED FLOW CONTROL VALVE

Since the flow through an orifice is essentially proportional to the square root of the pressure drop ∆p across it. This means that any appreciable change in the work load would affect the speed.

To overcome this problem one is made of pressure compensation device. A hydrostatic is utilized to maintain a constant pressure drop across an adjustable throttle.

Since flow through a pressure compensated flow control valve is subject to change with variation in oil temperature, so a temperature compensating rod which lengthens when hot and contracts when cold is incorporated in valve. The throttle is simpler plunger that is moved in and out of the control port. The compensating rod is installed between the throttle and its adjuster. Viscosity of oil decreases with temperature tending to flow freely, but the throttle opening is also reduced with the help of compensating rod.

A reverse free-flow check valve is also included in the valve. A schematic representation and internal construction is shown in the given figure…..

PRESSURE RELIEF VALVE

The pressure relief valve limits pressure in the system to a preset maximum by diverting some or all of the pump’s output to tank when the pressure setting is reached. It is a infinite positioning valve i.e. the valve can assume various position between fully closed and fully open, depending on flow rate and pressure differential.

It consists of a ball held seated in the valve body by a heavy spring. When pressure of inlet is insufficient to overcome the force of spring, the valve remaining closed. Then the preset pressure is reached, the ball is forced off its seat and allows throw out the outlet to tank for as long as pressure is maintained. An adjusting screw is provided to vary the spring force. Thus the valve can be set to open at any pressure within its specified range. The valve is shown in the given figure…

PRESSURE REDUCING VALVE

Pressure reducing valves are normally open pressure controls used to maintain reduced pressure in certain application. They are actuated by pressure sensed in the branch circuit and tend to close as it reaches the valve setting, thus preventing further build up.

It is self operated type valve. The spring force on one side is opposed by a pressure on the other side. Rising system pressure acts against the spring to close the flow path. The leakage oil is internally vented to tank with all valves. If the valve closes completely, leakage past could cause pressure to build up in the branch circuit, so a continuous bleed to tank is permitted to keep it slightly open, and prevent downstream pressure from rising above the valve setting. A drain passage is provided to return this leakage flow to tank.

A direct acting pressure reducing valve is shown in the above figure...

HYDRAULIC MOTOR

Hydraulic motor converts hydraulic energy (pressure * oil flow) into mechanical energy (torque * speed). Hydraulic motors are of various designs. One type is gear motor. This consists of following main components:

1. Gear wheel set

2. Commutator valve with shaft

3. Drive

4. Housing

The gear wheel set has an outer ring which is built together with the housing with (n+1) internal teeth and an internal rotor with external teeth. The teeth of the ring and rotor are meshing together. The rotor has one tooth less then the ring, and this result in the so-called gear

wheel spaces between the ring and rotor. One half of these spaces are connected to the delivery side of motor. A simpler rotary flow divider valve guides the liquid in such a way that the delivery and return spaces rotate synchronously with the rotor. The drive forms the mechanical connection between the commutator valve and the rotor.

The rotor movement is the combination of rotation and translation. The drives have splines at either end and allow only rotary movement.

Pressure required in hydraulic motor depends on the torque load and displacement. A large displacement motor will develop a given torque with less pressure than a smaller unit.

CYCLINDER

Cylinder is a linear actuator i.e. output of a cylinder is straight line motion. It is classified as single or double acting. Single acting cylinder has only one fluid chamber and exerts pressure in only one direction. It is mounted vertically and retracts by the force of gravity. Head counterbalanced cylinders are of this type.

A cylinder consists of a barrel, a piston and rod, end cops and seals. Barrel is seamless steel tubing and piston is made of C.I. or steel. These cylinders also have provision for adjustable cushioning at both ends for smooth beginning and end of the stroke.

PRESSURE SWITCH

Pressure switches are used to make or break electrical circuits at selected pressures to actuate solenoid operated valves or other devices. They can be used to provide ON/OFF signal which can be fed into an electronic control system.

Movement of piston under pressure against a spring operates a micro switch. The spring is of corrugated diaphragm type. A restrictor is usually fitted in the pressure inlet to reduce the effect on the switch of any hydraulic shock loading in the system.

The pressure setting of the switch can be adjusted by turning an adjusting nut. A switching differential is provided in pressure switch. It means that switch will operate at certain pressure and above when pressure is being raised, but when pressure falls it will not operate at certain pressure lower than operating pressure. Difference is called switching differential and is essential to avoid tripping of machine frequently.

GENERAL INTRODUCTION TO ELECTRICAL AND ELECTRONICS ITEMS

1. Proximity Switches

Proximity switches are solid state switching device which required no physical contact to actuate them. These are use for control and positioning signals because of long life, high switching speed, no touch, zero operation force, wear and maintenance free operation, bounce free signal and reliable switching under extreme conditions. It comprises of three principle parts

i) Oscillator

ii) Trigger stage and

iii) Amplifier stage

To obtain a switching signal at given voltage and temperature, sensing distance (Sn) is the main factor. Sensing distance is the maximum distance between the target and the sensing face. Sensing face is the surface from which the electromagnetic field radiates.

Sn depends upon material, thickness and area of target.

Target diameter = Oscillator Unit Diameter

2. Limit Switch

Limit switches are used to make or break control circuit when mechanically actuated by a moving member. Moving member might be a dog mounted on the moving component, as in the case of travel or over travel limit switches, or may be of plunger actuated type as in case of filter clogged limit switch. The limit switch type may be of normally open type (NO) which will close when switch is actuated or normally close type (NC) which will actuated.

3. Circuit Breaker

A device designed to open and close by non automatic means and to open the circuit automatically on the predetermined overload of current, when properly, applied within its rating. Two types are there:

1) Thermal

2) Hydraulic

Thermal circuit breakers responds only to temperature change in the bimetallic element. Heat is generated in the element because of i2r losses. The element bends or deformed to open the contacts and unlatch the mechanism. Mainly used MCB (Miniature Circuit Breaker) offer dual protection i.e., protection against overload and short circuit.

MCBs are preferred over fuses as it disconnects supply instantaneously, and requires seldom replacement.

Some of the technical features of Circuit Breakers are:

Long mechanical and electrical operational life

High breaking capacity

Overload tripping through accurately calibrated bimetal strip.

Short circuit tripping through magnetic coil.

Circuit breakers gives protection to the equipments such as motors, transformers, air conditioners, refrigerators, geysers, mixers etc. and cables/wires in electrical distribution system.

4. Overload Relays

It can be defined as the device which is operative by variation in the conditions of one electrical circuit to affect another device in same or another electric circuit. Relays provides overload protection over control circuits when used in conjugation with contactors and other motor control equipments, they provide accurate and reliable control and protection under overload condition.

5. Contactors

Device used for repeatedly establishing and interrupting an electric power circuit. The contactors are suitable for controlling electrical circuit of all kinds e.g. capacitor, lighting, heating, switching A.C. circuit as well D.C. circuits Also suitable for use in control panel for machine tools, motor control centers and other applications where high frequency requirement is must.

Contactors should have following design features:

Long Life: Bounce free contact system contributes to long contact life.

Modern techniques of arc quenching: In case of A.C. contactor, double breaking contact divide the arc into two. For contactors of higher size, deionization chamber split the arcs into numerous short arcs.

Contactors are designs for very high frequency operation

Compact Size

Installation: Some contactors can be mount in any position and some with maximum inclination, from vertical surface, of 22 ½ degrees.

Auxiliary Contact: For control a interlocking purposes, contactors can be provided with a number of auxiliary contacts.

6. Fuses

A device used for protection of equipments. A wide range of fuses is available for protection of transformer, cables, capacitors and motors for application in Air or Oil.

HRC fuses are used for the interruption of fault current in indoor and outdoor high voltage system and also protection of distribution power equipment.

7. Pressure Switch

The function of pressure switch is to break or make the control circuit whenever the pressure actuates the switch contacts. The switch contacts may be normally open type which closes on increasing pressure or of normally close type which open on increasing pressure. Pressure switches use single pole double throw (SPDT) micro switches as switching element.

These switches are use with water, oil, air, nitrogen, inert gases, steam, mineral oil and natural gas etc.

8. Introduction to NC

Automation has been associated with advancement in technology. The problem of automation of small lot production have been overcome by numerical control (NC) machine tools have great extent.

NUMERICAL CONTROL (NC) is defines as “A system in which actions are controlled by direct insertion of numerical data at some

point. The system must automatically interpret at least some portion of this data.”

CNC

In CNC system, a dedicated computer is used to perform all the basis NC functions as per the control program also called executive program stored in the memory of the computer. It is this executive program, which makes it flexible/soft wired. Unlike NC systems, machine control data comes directly from the computer memory. Because of the memory availability user can store part programs also in computer. The capability to edit this part program is a real advantage to the part programmer right at the machine station. Additional features such as tape punching option, user oriented sub routine programs etc are also possible on CNC.

9. Feedback device

CNC system requires a measuring device and measurement can be done with feedback system. Basically feedback allows the control system to compare the machine’s actual position with command valve. The result of this comparison provides the ability of velocity and position control. Encoders, resolver or inductosyn are used as feedback devices.

Encoders

Incremental rotary encoder is most commonly used feedback device. The rotary encoder is a shaft-driven device delivering electrical pulses at its output terminal. The pulse frequency is directly proportional to shaft speed. Encoder consists of glass disc marked with a precise circular pattern of alternate clear and opaque segments on its periphery. The disc is mounted on the shaft. A fixed source of light is on one side and a photo cell is placed on other side of the disc. As disc rotates, light is permitted to fall on photo cell, to produce the output signal which is approximately sinusoidal. Internal or external amplifier is used to amplify the photocell output to a level suitable for feeding logic circuits. Amplified signal is fed to a circuit which converts the signal to a proper square wave with suitable rise and fall

times. To sense direction of rotation a two photocell system is used. Photocell is arranged so that output signals have 900 shifts to each other. External logic circuitry is used to determine the direction of rotation.

10. Drives

Drives refer to the system package compared to servo amplifier and servo motor.

10.1 Spindle drives

The spindle drives on modern NC machines is DC/AC drive. It is used in combination with three or four step gear boxes to get full power in the entire cutting speed range. These drives are controlled by SCR/Transistor controllers.

10.2 Axes Drive

All axes are driven by DC/AC servo drives controlled by SCR/transistors through pre-loaded balls screw and nuts. Vertical slides are normally equipped with hydraulic counter balance to provide smooth servo action. As cent percent counter balance will not always be possible, spring set disc brake is used on servo motor to hold the position of the vertical slide during shut down of machine.

10.3 D.C Motor

A D.C. motor can be thought of made up of two parts:

1) A stationary field either of permanent magnet or electromagnet

2) An armature which is allowed to rotate.

The armature consists of series of coils which are connected to motor’s commutator and brushes. The commutator serves to switch the power to successive coils as the armature rotates so that magnetic armature poles remain in the same position relative to the field poles. As the armature rotates in the magnetic fields the motion of its conductor generates a voltage. This is true whether motor is delivering the power or driven by some external means.

10.4 D.C. Drive

D.C. drive controls motor speed through control of armature current by varying DC voltage applied to the motor. This is accompanied by controlling the point on AC input sine wave at which an SCR begins to conduct.

From diagram, speed, integrators regulator motor speed by summing both velocity reference and tachometer signals. An error signal between reference and feedback is then amplified and compensated for optimum controller response. Current regulator regulates the armature current by outputting a voltage signal to both the forward and reverse three phase firing circuits. This is accomplished by summing the current reference signal from output of the speed integrator with the current feedback signal from the motor armature. The resultant error signal is amplified and compensated for the electrical parameters of the motor.

Block Diagram description of DC drive

Forward and reverse three phase firing circuit control SCR gating. The SCR gate pulse is phase is pulse shifted and synchronized relative

to the AC line so that gated SCR produces a variable output voltage from the power bridge.

The regenerative power bridge converts three phase AC power to a controlled DC voltage capable of powering the motor armature. It’s out is fully controlled by forward and reverse three phase firing circuits.

Forward and reverse three phase synchronizers controls the time during the AC cycle when the forward and reverse three phase firing circuits can turn –ON an SCR.

Current limiter restricts limits the level of armature current reference. The level of restriction generally depends upon motor speed.

10.5 A.C Drives

DC thyristor Leonard control system driven by the DC motor is essential to perform the high precision-speed or torque control requiring quick response. Performance of AC variable drive system could not be equal to the Leonard system. But, it is necessary to maintain the for DC motors, because they have brushes and commutator. AC variable speed drive system consists of squirrel cage induction motors and inverters are maintenance free and easy

Block Diagram description of AC drive

operation. Recently high performance AC drive system which is frequency control on basis of vectrol was developed in order to realize the same quick response and high-precision speed control as Leonard System.

PRINCIPLE OF TORQUE GENERATION

The mechanism of torque generation is the same in the D.C. motor and squirrel cage induction motors. Excellency of performance of the D.C. motor (separately-excited and shunt winding type) is due to the fact that magnetic flux and armature current are supplied separately, that the armature current is held always in such a relation as to be perpendicular to flux by a commutator and brushes and also that torque and armature current are in proportion to each other under the condition of constant magnetic flux at any moment.

However, in squirrel cage motor, primary current is only supplied to the stator winding from power supply. The torque is produced by magnetic flux caused by this and torque current component (corresponding to armature current of D.C. motor). Although the mechanism of torque generation is stable under the steady state condition, the induction motor cannot quickly obtained the stable response at the moment that load or reference value are suddenly changed, that is, under the transient condition.

10.6

No commutator, so maintenance easier, electronic inverter serves the purpose of commutator.

Advantages of brushless A.C. motor over D.C. motor

Low inertia due to high flux permanent magnets.

Wear and tear less.

A.C. motor weights 35% to 65% less than D.C. motors are 20% to 30% shorter and 10% to 20% smaller in diameter.

Information is stored in digital form as drive is micro-processor based, so better control over tuning the drive.

Inside fixed encoders for both position as well as speed feedback signal.

Size of transformer is reduced as power supplied required is line voltage.

High peak/continuous ratio. High torque at full speed.

High rate of speed and acceleration.

1) A.C. induction motors generally are not suitable for precise motor control. A tendency to cog at lower speeds is limiting factor.

Disadvantages

2) Torque is not directly proportional to a current, a requirement for good dynamic performance.

1) Axes position and velocity control

VARIOUS FUNCTIOS OF CNC

2) Spindle speed

3) Miscellaneous functions.

1.1 Various functional codes

1) Preparatory function: these are commands which prepare the machine for different modes of movements like position countering, thread cutting etc.

2) Dimensional Data: Movement of machine tool slides in one or more axes is determined by dimensional data entered in the program.

3) Miscellaneous Function: Some of the important miscellaneous function which worth to be considered here are coolant on or off, Spindle CW or CCW, program stop etc.

4) Speed Function(S): this function pertains to speed of spindle.

5) Feed Function (F): It pertains to feed rates of the slides.

6) Tool Function (T): this function pertains to the selection of required tool for the particular operation.

CODES USED IN CNC PROGRAMS

G-code is the name of any word in a CNC program that begins with the letter G and generally is a code telling machine tool what type of action to perform. Such as: Rapid Move etc.

Controlled feed move in straight line or are series of controlled feed moves that would result in whole being bored, a work piece cut (routed) to a specific dimension, or a decorative profile shape added to edge of work piece.

There are other codes; the type codes can be thought of registers in the computer

X absolute position

Y absolute position

Z absolute position

A position (rotary around X)

B position (rotary around Y)

C position (rotary around Z)

U Relative parallel axis to X

V Relative parallel axis to Y

W Relative parallel axis to Z

M code (another “action” register or machine code (*))

(Otherwise refers to as miscellaneous function)

F feed rate

S spindle speed

N line number

R arc radius

P dwell time

T tool selection

I arc data X axis

J arc data Y axis

J arc data Z axis

D cutter diameter

H tool length offset.

(*)M codes control the overall machine, causing it to stop, start, turn on coolant, etc., whereas other code pertain to the path traversed by cutting tool may use same code to perform different functions; even machines that use the same CNC control.

Code Description

COMMON FANUE G CODES

G00 Rapid positioning

G01 Linear interpolation

G02 CW circular interpolation

G03 CCW circular interpolation

G04 Dwell

G10/G11 Data writing/Data write cancel

G17 X-Y plane selection

G18 X-Z plane selection

G19 Y-Z plane selection

G20 Programming in inches

G21 Programming in mm

G28 Return to home position

G31 Skip function

G33 Constant pitch threading

G34 Variable pitch threading

G40 Tool radius compensation off

G41 Tool radius compensation left

G42 Tool radius compensation right

G81 Simple drilling cycle

G82 Drilling cycle with dwell

G83 Peck drilling cycle

G84 Tapping cycle

G90 Absolute programming

G91 Incremental programming

G94/G95 Inch per minute/Inch per revolution feed

G96/G97 Constant cutting speed/Constant rotation speed

M00 Program stop

BASIC ISO CNC CODES

M01 Optional stop

M02 Program stop

M03 Spindle CW

M04 Spindle CCW

M05 Spindle stop

M08 Coolant/Lubricant on

M09 Coolant/Lubricant off

M30 Program end

M98 Subprogram call

M99 Subprogram end

G96 Constant surface speed

G97 Constant spindle speed

G50 Maximum spindle speed

G95 Feed mm per revolution

G94 Feed mm/min

G00 Rapid movement

G01 Linear interpolation

F Feed

S Spindle speed.

PROGRAM OF B.C.M. AXILE

Roughing is already done.

Depth of cut is 1mm.

.%001

N435 G54 (I SET UP)

N440 G92 S300

N445 M25

N450 G0 X700 Z10

N455 T0707 (FINISH TOOL)

N460 G96 S160 M04

N465 M46

N470 G0X170 Z10

N475 G01 X155 Z2 F9

N480 X145.1 F.3

N485 Z-244.899

N490 X144.55

N495 G02 X179.1 Z-276.75 I38. F.15

N500 G01 Z-287.075 F.3

N505 X178.6

N510 G02

N515 G01

N520 Z-496

N525 G02 X184.1

N530 G01 Z-740

N535 G02

N540 G01 Z-953

N545 X215

N550 Z-1460 F9

N555 Z-244.899

N560 X144.55

N565 G02 X179.1 Z-276.75 I38. F.15

N570 G01 Z-287.075 F.3

N575 X178.6

N580 G02

N585 G01

N590 Z-496

N595 G02 X184.1

N600 G01 Z-740

N605 G02

N610 G01 Z-953

N615 M24

N620 M30

%002

(2nd Set up)

N305 G54

N310 M25

N311 T1212(FINISH TOOL)

N315 G96 S200 M04

N320 G01 X146 Z5 F9

N325 X142.5 Z0 F.3

N330 X144.5 Z-12.7

N335 X135 F.4

N340 Z-245.292

N345 G96 S200 M04

N350 G01 X146 Z5 F9

N355 X142.5 Z0 F.3

N360 X144.5 Z-12.7

N365 X135 F.4

N370 Z-245.292

N375 X-287.075

N380 G03 X185.15 Z-297 I16

N385 G01 X186.7 Z-302

N390 X186.75

N395 Z-245.292

N400 G96 S200 M04

N405 G01 X146 Z5 F9

N410 X142.5 Z0 F.3

N415 X144.5 Z-12.7

N420 X135 F.4

N425 Z-245.292

N430 X-287.075

N435 G03 X185.15 Z-297 I16

N440 G01 X186.7 Z-302

N445 G01 X600

N450 Z50

N455 M24

N460 M30

There are different CNC machines in Jhansi unit, which serve some special purposes.

CNC MACHINES IN JHANSI UNIT

CNC OXY-ACETYLENE FLAME CUTTING

This machine is in bat-0 & is used for M.S sheet. This machine can cut up to 300mm thick sheet. It has four burners, which can work simultaneously.

• Control system : ESAB German (NCE-510)

• Axes: There are two axes in machine X and Y axis. In X axis tool can move up to 7 meters and in Y axis tool can move up to 3.5 meters

• Drive: D.C.

• Feedback rotary encoders

CNC CROPPING LINE

There are two cropping line CNC machine in bay-5. These are used to cut CRZO sheets for construction of core of transformer.

First machine has been made by George German with control system from Siemens 810D. This machine mainly consists of two tools: punch and swing shear for cutting lamination as required by program.

The other machine has been manufactured by Sooner Company. It has two punches. One fixed shear and one movable shear, which can shear straight as well as 45 degree. It consists of one tip cut and one V cut also.

(a) Control System 810D

(b) Axis: One axis

(c) Drive Way

(d) Feedback linear Scale

ASQUITH CNC BOGIE MACHINE CENTRE

This machine is in boogie shop. it is used for all operation in boogie manufacturing like milling, drilling and boring. All the operation can be done in the single machine.

CONTROL SYSTEM : GE FANUC 15M

Axis: It works three axis X, Y and Z axis. It can travel up to 8000 mm in X-axis. 4000 mm in Y-axis and 800 mm in Z-axis.

Feedback linear scale.

It has auto tool changer, which can change tools automatically. According to program its spindle diameter is 180 mm and 40 KW power is required to operate the spindle.

(A)HMT SB CNC LATHE

This is used for turning the job.

1) Control system: Sinumeric 3T

2) Axis: It works in two axis X and Z axis. Tool can traverse up to 1000 mm in X-axis and 300 mm in Z-axis.

3) Drive D.C.

4) Feedback: Rotary Encoder.

(B) HMT CNC VERTICLE MILLING MACHINE

This machine is used for milling purpose.

1) Control system : Sinumeric 800 M

2) Axis: it works in three axes X, Y and Z axis. Tool can travel 1200 mm in X-axis, 600 mm in Y-axis, 400 mm in Z-axis.

3) Drive D.C.

4) Feedback rotary encoder.

(C) COOPER CNC VERTICLE BORING MACHINE

This machine is used for boring purpose.

1) Control System: Cruceder

2) Axis: Tool can move in two axes: X and Z- axis. It can move 600 mm in X- axis and 400 mm in Z-axis.

3) Drive D.C.

4) Feedback : Linear Sale

1. Productivity

ADVANTAGES OF CNC MACHINES

Since cutting tool is brought to its machining position much more efficiently than it was done manually by the machine operator, NC machine is spending much more time per shift cutting than in past. Conventional machines very seldom remove metal for more than 15% of total available time under normal batch production conditions. Whereas CNC machine tools should be capable of removing metal for between 50% and 75% of available time. When working on medium batch production, CNC machining has around 4 to 1 productivity advantage over conventional machine. The actual productivity

advantage may vary from batch to batch depending upon the complexity of components to be produced and is normally proportional to the number of conventional operation required to produce the components.

2. Flexibility in design and production

Machine can switch over to different job as set up times are low and sudden changes in sales requirement are much more easily catered for. This enables the formulation of more aggressive marketing plans. The use of CNC machines also give designers freedom to design components which, by conventional means, are often impossible to produce. Change of design can also be easily incorporated as it means change of tape.

3. Inspection

High position accuracies and repeatability are inherent features of CNC machines and reduce inspection time considerably.

Normally a 100% inspection of the first component produced by a new tape is all that is necessary to prove the tape and tooling. Subsequently it is required to have only sample inspection. In process gauging and inspection is also provided on modern CNC machines.

4. Floor space

One CNC machine can replace five to six conventional machines. Thus manufacturing activities of a company can be expanded without increasing the floor area proportionately.

5. Inventory

By using CNC machine, procurement sizes and batch sizes can be reduced because of shorter lead time’s .This results in substantial saving. Lead time is time taken to progress a batch of component through a batch of production shop and is proportional to number of operation required by conventional methods. For example a component which requires 112 set ups by conventional methods may requires only 1 or 2 set ups in CNC machining center reducing total product flow times.

6. Material Handling

Handling of component from machine to machine which is necessary on conventional machine is significantly reduced on CNC machine, as all the operations are performed on one machine. This obviously reduces labor cost.

7. Tooling

This ability to complete machine part in a single setup means that fewer and simpler fixtures are required, which in turns requires less storage space and maintenance. The simpler a fixture is, the less expensive is to manufacture it.

8. Operator’s Skill

Dependence on skilled labor can be dispensed with. The accuracy of part produced with CNC machines machine depend upon accuracy and ability of machine and tape – and not on individual operator.

9. Scrap and Rework

Drastic reduction in scrap is achieved because of the inherent accuracy and repeatability of CNC machine.

10. Costing

Time required to produce a component is a function of machining cycle of CNC machines and is not influenced by operator’s efficiency or variation in labor’s rate, a great stability of prices can often be achieved throughout the life cycle of the respective product. Also cost accounting becomes very precise.

11. Better Management Information and Control

With various advantages of CNC machines, decisions effecting unit cost, delivery and quality are firmly placed in the hands of management and not of the machine operator.

It is true that CNC machine costs more to install initially. But higher initial cost is set off by the direct and indirect gains resulting from various advantages of CNC machines. In most cases, careful techno-economic evaluation of a given manufacturing situation will clearly bring out that unit cost of production is definitely less tools with that of so called conventional machines.

CONCLUSIONS

To conclude numeric control is the most sophisticated form of automatic control of machine tool. It has high degree of precision and reliability. The control system has undergone several stage of development.

Some of the special features offered by CNC machine manufacture are:

Thermal stabilization

Axis calibration

Lost machine compensation

With the various above qualities of CNC machine there are numerous advantages. They are

High accuracy

High reliability

Less scrap and network

Better machine utilization

Computer control of manufacture capability of integration into distribution numeric control (DNC) etc.

The programs written for CNC are easy to write and understand. These programs use either G-cod or M-code that runs the program. The codes are simple to understand.

No wonder CNC machines tools are becoming more and more popular day by day in modern industries. In longer run CNC machine pays for itself with such outstanding qualities.

Bibliography

1. CNC Programming handbook by Mr. Peter Smid.

2. Managing CNC operations by Mike Lynch

3. Wikipedia.

www.wikipedia.org/wiki/Main

4. B.H.E.L. official website

http://www.bhel.com/home.php

5. CNC information and easy CNC by Mr. David Benson.

6. http://www.cnccncmachines.com

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